B50 oil pressure switch removal

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Armstrong Phil
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B50 oil pressure switch removal

Post by Armstrong Phil » Mon Aug 31, 2020 10:31 pm

My new B50 came with an oil pressure switch fitted. From what I understand as it's a roller bearing engine it doesn't generate much oil pressure. On my way home from collecting it on a very hot day the warning light kept coming on causing some concernation. A quick check to confirm oil was returning and I carried on without issue. I intend to remove the switch, but have been unable to find a blanking plug with the same thread, anyone know where I can get one?

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SteveS
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Re: B50 oil pressure switch removal

Post by SteveS » Tue Sep 01, 2020 8:27 am

Hi Phil

Part number is 70-9526 and I believe the thread is 1/8" bspt.

Yes. :thumb just found a previous thread here confirming details.

You should be able to find a source for the plug fairly easily.

Here's a nice shiny one 1/8" BSPT Male Stainless Steel Countersunk End Plug Internal Hex Head Socket

or a pack of 4 black iron plugs, much cheaper - 1/8 BSPT x 3/4 Pressure Plug Self Colour Pack (4)
Steve Sewell

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Re: B50 oil pressure switch removal

Post by Armstrong Phil » Tue Sep 01, 2020 1:37 pm

Thanks Steve, I'll get one ordered, looking at that thread I' m not the only one who was confused!

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Re: B50 oil pressure switch removal

Post by JB » Tue Sep 01, 2020 6:02 pm

Go careful with this, only going from memory although I'm fairly certain that Lucas used an American 1/8 NPT thread on their oil pressure switches, not BSPT as you'd have expected :shock:
Similar to this one https://www.ebay.co.uk/itm/Oil-pressure ... 1195.m1851

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Re: B50 oil pressure switch removal

Post by Jeff K » Tue Sep 01, 2020 6:50 pm

Is it a tapered or straight thread? I seem to recall that Triumph Triumph T100 twin used both. I am not sure if BSA did also, I know that BSA and Triumph shared a lot of parts. Getting them mixed up will cause issues.
Jeff

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Re: B50 oil pressure switch removal

Post by SteveS » Tue Sep 01, 2020 8:04 pm

Just pulled the plug out of a spare B50 inner cover. Definitely a tapered thread. My thread gauge jumps from 26 tpi to 28 tpi. My eyesight is too poor to check tpi accurately but I would say the 26 tpi is a better fit than the 28.

1/8bspt is 28tpi, npt is 27tpi, taper is 3/4" per foot for both thread types

The plug is 8mm long (5/16")
Diameter is 10.0mm tapering down to 9.75mm

Not sure if my measurements allow anyone to draw an accurate conclusion
Steve Sewell

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Re: B50 oil pressure switch removal

Post by Armstrong Phil » Tue Sep 01, 2020 11:11 pm

Sounds like I've opened a can of worms! Think I'll take the switch out, cut the head off and drill tap it for a sealing bolt and use that, at least I know I've got the right thread and won't damage the case.

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Re: B50 oil pressure switch removal

Post by Jeff K » Tue Sep 01, 2020 11:21 pm

Armstrong Phil wrote:
Tue Sep 01, 2020 11:11 pm
Sounds like I've opened a can of worms! Think I'll take the switch out, cut the head off and drill tap it for a sealing bolt and use that, at least I know I've got the right thread and won't damage the case.
:thumb :thumb

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Re: B50 oil pressure switch removal

Post by JB » Tue Sep 01, 2020 11:35 pm

Lucas pressure switch Thread is NPT... not BSP.
You will be able to fit a BSP thread although it will damage the thread in the casting.

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